Tuul Sepp & Elin Sild
A stork has adopted a concrete electric post as its nesting place.
Swallows gather to sit in rows on electric wires before migration.
A colony of common gulls has occupied the roof of the kindergarten building.
Swans, common coots and other waterfowl have used plastic bags, pieces of rope and other plastic packaging to build their nests.
Humans have reshaped almost all of the Earth's habitats and man-made materials have found their way everywhere in nature. When walking along a forest trail, it does not take long to come across a glass bottle or an old tin can. Asphalt roads cut through natural habitats. One of the most widespread micro-objects in the Baltic Sea is blue fiber – the product of the degradation of polypropylene ropes.
What kind of relationship do birds have with artificial materials? Birds have more choices, but less opportunities. While natural habitats are diminishing, new evolutionary options have emerged to use man-made materials for building a nest, promoting one's skills, eating and feeding offspring, as well as using as habitat. Unfortunately, the declining numbers of birds show that this increase in choice does not always compensate for the lost opportunities.
It is possible to learn to use the new evolutionary items. In a changing environment, the ability to learn is a prerequisite for adaptation. A well-known example of this are the British blue tits, who learned to open the foil tops of milk bottles left on doorsteps by milkmen. Yet, learning comes at a price. The bird can learn a bad thing which leads to short term benefits but turns out to be harmful in the long run. Learning is also consuming, wasting time and resources that could be used for something more enjoyable. The novel environment and new materials challenge the birds’ abilities to learn and adapt.
It is also possible to learn not to use the new evolutionary options. Getting to know the dangers of artificial materials is risky. The negative experiences from learning must not result in death for the birds. If the risk related to the artificial material is very high, posing a threat to the bird’s life, then learning becomes impossible. None of us gets a second chance where life is concerned.
The inviting artificially smooth open space of highways is an evolutionary dead end for birds, from which it is hard to escape. The European nightjar, Estonia’s bird of the year 2019, who likes to rest and enjoy its food on the roads, is one sad example – many nightjars get killed on the roads. I recently found a green sandpiper on the streets of Tartu, where it had been hit by a car. The artificial clearings created by roads and streets are not equal to forest glades, but for birds it is difficult to learn the difference.
Can a bird really see a wide highway as an analogue for a natural glade? Let's take a look at the man-made world through the eyes of the birds. The city with its high-rise buildings is like a landscape full of steep cliffs – a suitable habitat for domestic pigeons descended from rock doves. The roofs of the houses are similar to islets in the sea, where the fox and the raccoon cannot access the seagull’s nests. Electric posts and electric wires are like trees with straight inviting branches that extend for tens and tens of kilometres. Plastic bags are light and waterproof material suitable for nest building. Pieces of rope, straws and plastic elements are like twigs, which are easy to use and handy (or pecky) to entwine into the structure of the nest.
Why use artificial materials instead of natural ones? There are habitats where man-made material is easier to find than natural sticks and straws. In the city parks and in the street gutters, all the dried straws and leaves get raked up with embarrassing attention, taking away natural materials that could offer a valuable winter habitat for insects and suitable nesting material for birds next spring.
People often see natural materials in the urban space as a sign of chaos, uncontrollability, being taken over by nature. Artificial materials demonstrate the triumph of order over chaos; man's victory over the entropy of nature. If there is nature in the city, it must be controlled: the grass mowed to a height of exactly 5–7 cm, the leaves raked, the bushes pruned. The garden plots must have straight edges and flower beds must be in concrete boxes.
Nature seems threatening. Predators, diseases, strangers and the unknown lurk there. Urban life has its own often bigger health threats but as they are new in evolutionary terms, we are not afraid of them yet. This is not specific to the human race. For many birds that have moved to the city, the urban habitat represents an opportunity to leave behind the parasites and diseases, natural predators and competitors of their native habitat. The city is not necessarily a bad habitat for a bird. It depends on the species whether the bird can also benefit from urban life.
Some birds are survivors in the man-made environment. They have always occupied this area, even before the changes brought about by humans. They do not leave, they adapt. They get by, they survive, they suffer through it. The surviving species are different in different parts of the world, as they are local species who remain after the formation of cities, even though in smaller numbers than in the original, natural environment.
Then there are also the exploiters. Birds who enjoy the man-made environment. They manage better here than other species; the city gives them a competitive advantage. They move to the city and prefer the city to the natural habitat. Exploiters are characterized by a wide choice of food (they are not specialized on one food only), large brains (which enable them to problem-solve and learn) and flexibility in the choice of a nesting place. Exploiters include, for example, sparrows, jackdaws and crows.
It is worth noting that while the number of species of birds decreases in rural areas, then in cities it shows signs of growth. This could mean favourable outcomes for birds, but not always. For some species, the man-made landscapes and materials turn out to be an ecological trap. They attract, but they are also dangerous.
The survival and reproductive success of trapped species decreases while using man-made materials. At the same time, they cannot resist it as evolution has not provided them with the means to recognize and avoid these novel dangers. For example, the pieces of film woven into a waterfowl's nest may raise the temperature of the nest to a level unsuitable for the development of the fragile fetus taking shelter inside the egg, likewise the chicks may get entangled in the pieces of plastic ribbon or eat the plastic bits.
When the artificial material is available, it is generally also used despite all the hazards. Northern gannets use considerable amounts of marine litter for building their nests. However, if the beaches are more diligently cleaned, less artificial materials and more natural ones are found in the nests of northern gannets. The more plastic waste there is, the more it gets used in building nests. The northern gannets do not have the ability to consciously avoid plastic waste. Yet, humans have the ability to control their waste production and clean up after themselves.
There is another side to the coin, however. Seemingly harmful materials can sometimes turn out to be beneficial to birds. Some birds have learned to install cigarette butts in their nests in order to repel the parasites living there. The materials and objects stolen from humans can help to impress possible mates, giving proof of the bird’s skill and sense of beauty. There is a reason why magpies steal shiny objects.
The satin bowerbirds in Australia, who prefer to decorate their dance arenas with blue objects to attract their mate, are able to make their bowers particularly eye-catching with blue bottle caps and straws. Some bird species are even heavily into innovation. And what is there to wonder? There was a time, during the shortages at the end of the Soviet era, when colourful plastic bags were also status symbols among Estonians.
When a bird starts using artificial materials or artificial spaces, there is always the possibility to find their analogues among natural materials and places. An electricity post is similar to a tree growing in a glade. The electric wires are like branches. The highway like a clearing. The plastic waste and pieces of string like branches and straws. Through the eyes of birds, the artificial materials find a new role in the natural environment, the artificial world transforms again into the natural realm, chaos triumphing over order.
The decay of the artificial moves life forward through ancient solutions tried out by natural selection. The purpose of life is to survive and procreate, other purposes lose their significance and do not have the strength to survive through evolution.
What part of the artificial materials created by humans supports these purposes for humans and for other species? This is a key question when we look around the man-made world and ask ourselves what remains of this after thousands, hundreds of thousands and millions of years.